1. Field of the Invention
The present invention relates to a position detecting device suitable for use in handling a workpiece by a robot for an operation of taking out workpieces stacked in multiple stages or piling up workpieces successively, and takeout apparatus using the position detecting device.
2. Description of Related Art
In an operation of taking out workpieces stacked in multiple stages successively by a robot, the number of stages of the stacked workpieces and thus a position (particularly in a height direction) of the workpiece to be taken up change. In such a case, a sensor is used to recognize the position of the workpiece to be taken up. In this case, it has been deemed to be difficult to recognize the number of stages or height of the stacked workpieces based solely on information obtained by a two-dimensional image capturing device such as a camera.
For this reason, the detection of the number of stages of the workpieces has been realized by methods such as one that uses a contact sensor for measuring height of an upper surface of the stacked workpieces, one that utilizes a so-called stereograph to detect the height of the workpieces based on images captured by two or more cameras, and one that uses a projection of a plurality of slit lights on the workpieces to obtain a three-dimensional image of the workpieces.
However, use of the contact sensor for measuring height of the stacked workpieces has a problem of failing in contact with the upper surface of the workpieces if the workpieces are displaced in a horizontal plane. Thus, in order to avoid this problem, it is necessary to use a two-dimensional visual sensor in combination with the contact sensor. In addition, the method of the stereograph also has problems of need for installation of a plurality of cameras and processing for establish coordination between a plurality of images captured by the plurality of cameras is required for realizing the detection of height of the stacked workpieces, and a difficulty in establishing the coordination.